OBJECTIVE: Evaluate the role of bone marrow transplantation in the treatment of acute and chronic leukemia, solid tumors, aplastic anemia, and genetic disorders such as immunodeficiency diseases and thalassemia. APPROACH: Several approaches are being evaluated in these diseases. These include: 1. Transplantation from HLA-identical siblings in patients with acute leukemia in remission. 2. Autologous marrow transplantation in patients with leukemia. 3. Phase 1-3 trials of marrow autotransplantation in patients with solid tumors. 4. Studies of alternative sources of hematpoietic stem cells for transplantation. RESULTS: Results are summarized by treatment group: 1. 50-70 percent long-term disease-free survival in severe aplastic anemia. 2. 50 percent 2-year disease-free survival in acute leukemia in remission. 3. 50 percent response rates in patients with resistant solid tumors receiving marrow autotransplants.